In recent years, there have been increasing demands for higher density magnetic recording media. Particularly in video tapes, recording in very high density as well as in higher frequency range has been desired. With this background, various designs have been proposed, in which the support is coated with a magnetic layer comprising two layers (upper and lower layers) or three or more layers (hereinafter referred to as a multilayer structure).
Japanese Patent Publication Open to Public Inspection (hereinafter referred to as Japanese Patent O.P.I.) Nos. 56228/1983, 56230/1983, 70429/1983 and 98135/1982 disclose the methods of increasing multilayer tape density in which the BET value and grain size in each of the upper and lower magnetic layers are controlled.
However, significant improvement in electromagnetic conversion properties of multilayer tapes cannot be expected even when the BET value of the magnetic substance is increased or the grain size is decreased, unless the loading rate of the magnetic substance in the magnetic layer is optimized.
Japanese Patent O.P.I. Nos. 69528/1982, 20042/1983 and 31018/1987 and Japanese Patent Examined Publication No. 8286/1979 disclose the methods in which the content and loading rate of the magnetic substance in each of the upper and lower layers are increased.
However, in these methods, an actual loading rate of the magnetic substance is liable to be lower than expected due to the pores in the magnetic layer since the content and loading rate are calculated on the basis of the weight ratio of the magnetic substance to the solid matters in the magnetic paint. This often leads to lower electromagnetic conversion properties than those expected from the sufficiently high loading rate in calculation. For this reason, these methods are inappropriate for the representation of the content and loading rate of the magnetic substance.